UC Riverside

Locomotion is an integral component of the majority of behaviors that dictate the survival of vertebrates. However, the environments through which animals move are often heterogeneous. The arboreal habitat may be one of the most challenging environments due to its wide variation in substrate incline, diameter, compliance, and texture. This array of structural challenges places extreme and varied demands on the locomotor system that muscles, as the units that power this system, must be able to cope with. Although we have a good understanding of the kinematic and neuromuscular modifications employed by animals encountering different inclines, we know virtually nothing about how other structural challenges affect locomotor behavior and in vivo muscle function. In this dissertation, I used a combination of high-speed video, electromyography, in situ contractile experiments, and morphology to understand how arboreal Anolis lizards modulate their behavior and power cyclical locomotion on surfaces of varying incline and perch diameter. Several significant results emerged. First, the forelimb and hind limb were modulated differently in response to changes in substrate; the forelimb likely adopts a greater propulsive role and the hind limb a more stabilizing role on steeper inclines and narrower surfaces. Second, there was a decoupling of the response of limb movements and motor patterns to changes in substrate; perch diameter had a stronger effect on kinematics than incline, whereas muscle activity was more strongly affected by incline than by perch diameter. Third, not only does muscle recruitment, operating length, and capacity for force production change with perch diameter to allow the gastrocnemius, a primary ankle extensor, to contribute more to propulsion on broader than on narrower surfaces, but incline appears to alter the relationship between muscle recruitment and efficiency of force production. Finally, hind limb tendons do not appear to have the potential to stretch and store significant elastic energy during cyclical locomotion in Anolis lizards. Together these data force us to acknowledge the complex nature of mechanisms that power locomotion in the natural world. The environment can clearly have a profound impact on both the coordinated function of limbs and the neural control and physiology of the muscles that power locomotor behaviors.